MacColl R, Guard-Friar D, Ryan T J
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
Biochemistry. 1990 Jan 16;29(2):430-5. doi: 10.1021/bi00454a018.
A series of experiments on the light-harvesting properties of the cryptomonad biliprotein phycoerythrin 566 has been carried out on purified protein isolated from Cryptomonas ovata. Although this pigment has an absorption maximum at 566 nm, a property very close to that of other phycoerythrins, it was found to have a totally unique set of chromophores. The chromophores (bilins) responsible for its absorption spectrum were analyzed by a number of approaches. Chromophore-containing peptides were produced by trypsin treatment and purified in order to isolate the individual peptide-bound bilins free of overlapping absorption. These chromopeptides, after comparison with appropriate controls, showed that three spectrally distinct bilins occurred on the purified oligomeric protein. Two of the bilins were the well-known phycoerythrobilin and cryptoviolin, but the third was previously undiscovered and had an absorption spectrum between that of cryptoviolin and phycocyanobilin. Since the spectral diversity of the three bilins was fully maintained in solvents that minimize the effects of apoprotein on the spectra of the bilins, it is likely that the three bilins are also structurally dissimilar. The alpha and beta subunits, which constitute the protein, were separated by ion-exchange chromatography, and the new bilin was found to be the sole chromophore on the alpha subunit. It was also found that at least two alpha subunits could be separated and they both had this unusual bilin (cryptobilin 596). The beta subunit, therefore, contained both phycoerythrobilin and cryptoviolin. On the basis of the spectra of the three chromopeptides, the absorption spectrum of the protein was modeled using the known absorptivities of cryptoviolin and phycoerythrobilin.
对从卵形隐藻中分离出的纯化蛋白进行了一系列关于隐藻双蛋白藻红蛋白566光捕获特性的实验。尽管这种色素在566nm处有最大吸收峰，这一特性与其他藻红蛋白非常接近，但发现它具有一套完全独特的发色团。通过多种方法分析了负责其吸收光谱的发色团（胆素）。通过胰蛋白酶处理产生含发色团的肽并进行纯化，以分离出没有重叠吸收的单个肽结合胆素。将这些发色肽与适当的对照进行比较后发现，在纯化的寡聚蛋白上出现了三种光谱上不同的胆素。其中两种胆素是著名的藻红胆素和隐藻紫素，但第三种是以前未发现的，其吸收光谱介于隐藻紫素和藻蓝胆素之间。由于在使脱辅基蛋白对胆素光谱影响最小化的溶剂中，这三种胆素的光谱多样性得到了充分保持，因此这三种胆素在结构上也可能不同。构成该蛋白的α和β亚基通过离子交换色谱法分离，发现新的胆素是α亚基上唯一的发色团。还发现至少可以分离出两个α亚基，并且它们都含有这种不寻常的胆素（隐藻胆素596）。因此，β亚基同时含有藻红胆素和隐藻紫素。根据这三种发色肽的光谱，利用隐藻紫素和藻红胆素的已知吸光系数对该蛋白的吸收光谱进行了建模。
